The invention relates to an interlock arrangement whereby one circuit interruption device such as a molded case circuit breaker or electric disconnect switch can be operated at one time. In a motor control cabinet whereby a plurality of circuit breakers are remotely driven by electrical motor operators, it is difficult to ensure that only one such circuit breaker or switch will be energized at one time. This is especially important when one such circuit breaker connects with a source of electricity from a utility supplier and the other connects with an auxiliary or emergency power source. Energization of two separate sources of power can seriously damage electrical equipment connected within the associated electrical power distribution system.
U.S. Pat. No. 4,924,041 entitled "Universal Circuit Breaker Interlock Arrangement" provides excellent interlock function between circuit breakers that are rated in excess of 250 ampere continuous current. With lower-rated circuit breakers such as those described within U.S. Pat. No. 4,754,247 which incorporates auxiliary apparatus within the circuit breaker cover, the compact circuit breaker operating mechanism responds rapidly to turn the circuit breaker contacts ON and OFF with a very short distance of travel of the circuit breaker operating handle. When the interlock arrangement, described within the aforementioned U.S. Pat. No. 4,924,041 is used with such smaller ampere-rated circuit breakers, it is possible to "tease" one circuit breaker to its ON position while the other circuit breaker is also in its ON position. Such an interlock arrangement for lower ampere-rated circuit breakers is preferably limited to manual operation since an operator can observe both handles within the interlock arrangement to insure that one of the handles remains OFF when the other handle is turned ON. With remotely controlled electric motor operators such as those described within the aforementioned U.S. Pat. No. 4,924,041, the movement of one handle of the interlock device to its ON position can cause the circuit breaker operating mechanism to rapidly switch the circuit breaker to its ON position before the other circuit breaker has fully turned to its OFF position because of the abbreviated handle stroke, as described earlier.
One purpose of the instant invention accordingly is to provide a circuit breaker interlock arrangement for lower industrial-rated circuit breakers whereby both of the interlock circuit breakers can be turned OFF at any time while only one of the interlocked circuit breakers can be turned ON at any one time.